After manufacturing a wind turbine rotor blade, the blade may need to be transported to a short-term or long-term storage facility, and ultimately the blade will be transported to an installation site, for example at an offshore windfarm. Transport modes can include ship transport or road and/or rail transport over land. For a wind turbine with a rated power output of several megawatts, a rotor blade can have a length in excess of 75 m, and may weigh several tons. Generally, a wind turbine rotor blade comprises a circular root end for mounting to a pitch interface of a hub. The root end of a blade for such a large wind turbine can have a diameter in the range of 2.0 to 4.0 m or more. The circular shape of the root end undergoes a transition towards the blade airfoil portion, which accounts for most of the blade length. The airfoil portion is generally widest close to the root end, and tapers to a narrow end or tip. The airfoil section of the blade has a rounded leading edge and a relatively sharp trailing edge. Between the leading edge and the trailing edge, the airfoil section has a curved convex upper surface (the “suction” side), and a curved concave lower surface (the “pressure side”). The unwieldy shape and dimensions of a wind turbine rotor blade make transport difficult. Furthermore, the blade is quite vulnerable to damage and must therefore be treated with care throughout all transport and handling stages to ensure that the surface remains smooth and intact.
The own weight of a rotor blade may present a problem during a lifting manoeuvre. For this reason, it is generally preferred to bring the blade into an “upright” position, i.e. a position in which the airfoil is essentially “vertical” or upright with the leading edge of the blade underneath and the trailing edge on top, while the blade itself is suspended horizontally from root end to tip end. This blade orientation also helps ensure that the vulnerable trailing edge of the blade is protected from damage, while the relatively straight leading edge has sufficient structural strength to prevent the blade from bending while suspended in the air.
During a storage or transport stage, several rotor blades may be arranged in an array of stacked frames. To fit many blades into a relatively small volume, the blades may be “inter-leaved” with the tip ends of some blades facing towards the root ends of other blades. Such a stacking arrangement must consider the height difference between the root portion of a blade and the relatively flat and narrow airfoil portion near the tip end. Furthermore, a blade should be stored so that it is not distorted by its own weight.
Between manufacture and installation of a rotor blade, it must be moved and handled several times, for example from a manufacturing facility to a storage facility, from storage to truck, from truck to ship, etc. Each handling stage may involve a change in orientation of the blade for the reasons given above. Furthermore, the blade must at all times be securely connected to any holding, lifting, hoisting or transport means. This may involve transfer between different holding means, for example because of different mounting structures or connection interfaces of a storage means and/or a transport means. Such connection procedures are time-consuming and costly and can significantly add to the overall costs of a wind turbine.